This is a biobehavioral, longitudinal investigation of the role of emotion in the development of psychopathology in adolescence. The focus is on (a) the role of multiple components of negative emotions (anger, anxiety, sadness) in the evolution of psychopathology, and (b) socialization experiences and biological processes that contribute to emotion dysregulation and disorder. The dysregulated experience and expression of emotion is implicated in both externalizing (antisocial patterns) and internalizing (anxiety, depressed mood) disorders. Adolescence is a critical juncture in the development of these disorders. The incidence of psychopathology increases during this time period, and clinical problems become more differentiated along gender lines, i.e. more antisocial behavior in males and more anxiety and depression in females.Four groups of youths are studied: (1) comorbid externalizing and internalizing problems, (2) externalizing problems, (3) internalizing problems, and (4) asymptomatic. Youth range in age from 11 to 16 years and are studied at two time points, spaced two years apart. Equal numbers of males and females are studied in order to examine etiology of sex differences in symptoms, emotion regulation, and developmental changes in how disorders manifested. Findings from four current projects that focus on predictors of functioning of youth at the first time point of data collection are summarized next. (1) Males and females differ in relations between neurohormonal patterns and psychopathology. Boys with more anxiety-depression problems, and attention problems, have lower levels of testosterone, and their testosterone levels decreased more slowly across the day. Girls with more disruptive behavior problems display a steep decline in testosterone production across the day. (2) Gender moderates many significant associations between psychopathology (internalizing and externalizing problems) and affective and cardiac reactivity. Internalizing problems (anxiety and depression) in girls are associated with greater blood pressure reactivity. Externalizing problems are associated with less systolic blood pressure reactivity, especially for boys. (3) Differences in emotions and self-concepts of males and females help to explain their differential risk for externalizing and internalizing problems, respectively. Males view themselves more favorably than females on global self-worth, athletic competence, physical appearance, and romantic appeal despite rating themselves as less well behaved. Females show more guilt and shame than males, and they engage in more ruminative coping. Rumination refers to the individual&#8217;s persistent focus on depressive symptoms, without taking any action to reduce the distress, thereby contributing to continuation of depressed mood and diminished self-esteem. (4) Gender-based patterns of psychopathology can be linked to sex-roles and emotion socialization experiences. Masculinity in youth is associated with few internalizing problems, and femininity is associated with few externalizing problems. Sex roles in conjunction with parental punishment, neglect, and emotionality (as well as lack of discussion, empathy, and distraction) in response adolescents&#8217; negative emotions are powerful predictors of psychiatric symptoms. These studies highlight the importance of studying both biological factors and socialization experiences that influence the form of expression of psychopathology in adolescent males and females.